<!DOCTYPE HTML>
<title>Testcase, bug 1299736</title>

<div id="A" style="transform: translateX(50px)">
  <div id="B">
    <div id="C" style="position: fixed">
    </div>
  </div>
</div>

<script>
  document.getElementById("C").offsetLeft; // flush
  document.getElementById("B").style.transform = "translateX(50px)";
  document.getElementById("A").style.transform = "";
</script>
